Age Estimation: A Multidisciplinary Approach

Age Estimation: A Multidisciplinary Approach is the only reference in the field covering all techniques and methods involving age estimation from different perspectives in just one volume. The book provides comprehensive coverage of all aspects of age estimation: aging the living and the dead, human rights, and skeletal, dental, histological and biochemical techniques and methods available. Each chapter is written by internationally known expert contributors.

Age Estimation: A Multidisciplinary Approach is a one of a kind resource for those involved in estimating the age of the living and the dead.

• Presents a concentration of all techniques and methods involving age estimation in a single volume
• Provides a multidisciplinary approach that lends itself to researchers, practitioners and students from a variety of different fields
• Includes contributions by world renowned forensic specialists

• Language: English
• Publisher: Academic Press
• Release date: Apr 11, 2019
• ISBN: 9780128144923

Book preview

Chapter 1

Complexities and considerations of human age estimation

Sarah Ellingham¹ and Joe Adserias-Garriga²,    ¹International Committee of the Red Cross, Geneva, Switzerland,    ²Forensic Anthropology Center, Texas State University, San Marcos, TX, United States

Abstract

Age estimation is a crucial parameter in forensic and archeological context. Age-at-death estimation is essential to reconstruct a biological profile, and therefore increasing the chances of identifying of the remains. Assessing age in archeological collections from a specific site offers important information on the demographics of that population. In addition, age estimation in the living is an increasing issue due to the migration crisis that takes place in different parts of the world. Age estimation of the living and the dead can be approached by skeletal, dental, histological, and biochemical means. Modern technologies and clinical images, such as CT scans, magnetic resonance images, or radiographs, are proving to become valuable sources for contemporary population data. Moreover, advances in biochemical techniques have allowed to open a new approach for age estimation that can be applied to all age ranges. Human age remains a subfield of forensic sciences that is constantly advancing with the ever-evolving fields of application. Nonetheless, technical possibilities need to always be weighed against their limitations as well as ethical considerations before embarking on a forensic analysis. Research on age estimation will be challenging and engaging professionals from multiple disciplines, be it the physical sciences, sociology, psychology, ethics, and even the law, for some time to come.

Keywords

Age estimation; forensic; archeology; multidisciplinarity; ethics

1.1 Introduction

In the forensic sphere, the topic of age estimation is as old as the discipline of forensic anthropology itself, and has traditionally been linked to the analyses of skeletonized human remains as a part of biological profile estimation. Determining an individual’s age can bring forensic investigations one step closer to an identification; determining the age of archeological collections from specific sites can shed light on the demographics of entire populations, allowing invaluable insight into the life and death of past societies.

More recently, partly driven by the media coverage of the migration wave resulting from recent humanitarian crises, the public’s focus has been more and more driven toward the question of age determination of living individuals. In many parts of the world, births not being registered is not an unusual phenomenon. The lowest birth registration rates can be found in sub-Saharan Africa, with only 43% of births being recorded within the child’s first 5 years of life, with children of poor families and those living in rural areas being far less likely to be registered than their wealthier and urban living peers respectively. Even less, only 26.9% of sub-Saharan children, are issued a birth certificate [1]. Globally, 29% of births go unregistered, leaving millions of children unable to provide documentary evidence of their age.

Challenges also arise in countries subjected to war and occupation. One such example is Iraq, where thousands of birth certificates issued under the Islamic State are not recognized by the Iraqi government, leaving the affected children in legal limbo.

For these reasons age estimation is a hot topic in forensic science, which can be approached from different disciplines. At present, different research groups are developing new methods, implementing novel technology, and trying to increase the accuracy of the age estimates for both, the dead and the living. It is the aim of this chapter to outline the potentials and challenges the different approaches to age estimation entail.

1.2 Age estimation of the living

Undoubtedly, it is the question of age assessment of unaccompanied minors seeking asylum in Europe, which has been captivating the public’s and the media’s interest the most in recent years. Sykes et al. [2] conducted a 10-year review of trends in age estimation in 16 countries and reported the number of age estimations related to asylum seekers and refugees to have increased by 26% and 13%, respectively, during the assessed period. According to the EU law on asylum, individuals under 18 years of age are considered children and as such a group of vulnerable persons, to whom EU member states have several immediate obligations [3]. An individual’s proven identity including their chronological age is crucial to defining the relationship between a host state and an individual [4]. The 1989 Convention on the Rights of the Child [5], signed by 193 UN member states, sets universally agreed and non-negotiable standards on children’s entitlements and freedoms. The 1989 Convention further states that children seeking asylum in these states have the same right to education and health care as other children and are frequently protected from detention or being returned to their country of origin [6]. Failure to correctly identify an individual as a child has the consequence of them being deprived of their rights as set out in the convention. The accurate age estimation of refugees and asylum seekers is also paramount for the functioning of the Common European Asylum System and the Eurodac Information system, which requires all applicants of 14 years of age or more to submit their fingerprints [3]. As the advantageous treatment of minor asylum seekers makes the system prone to abuse, the age-assessment procedures are frequently incorporated into the asylum procedure, if the claimed age raises doubts with the authorities.

The majority of EU member states have legal provisions for the age estimation of unaccompanied presumed minors seeking asylum, however, the approach in each country differs [3]. Methods can include a mere examination of all available documentation, psychological evaluations and personal interviews as well as medical inspections. The latter can encompass radiological examinations of the dentition, the non-dominant wrist, or and/or the medial end of the clavicle, as well as physical examination of puberty development [3]. An analysis published by the European Migration Network highlighted inconsistencies in the practices of 22 EU member states using one or more of the methods to estimate age: 20 countries utilized interviews and documentation, 16 countries skeletal assessments, 10 countries dental assessment, 7 used physical assessments by a physician, and 5 psychological techniques [4,7].

In addition to the lack of consistency between, and sometimes within, EU member states, each of the applied methods presents their own complexities and limitations. Some member states, such as the United Kingdom, do not use ionizing radiation due to the fact it may be potentially harmful, its high cost, and insufficient reliability [3]. If utilized, the analyses of x-rays should only be carried out by trained radiologists, as the interpretation requires a specific expertise and an awareness of the error rates and limitations. Skeletal age is dependent on a variety of differing factors, such as ethnicity, genetics, endocrinology, nutrition, as well as socioeconomic and medical circumstances. Most commonly applied reference tables for age estimation are based on Caucasian populations, such as the frequently used Greulich–Pyle atlas [8] for hand and wrist maturity, which is based on a 1930s population of white Americans, or the 1950s Tanner-Whitehouse method [9], derived from a sample of a British middle-class population. Applying these or any other age-assessment methods to individuals other than from the population they were derived from decrease the accuracy, in some instances significantly, which limits or even compromises their applicability [6]. Other limitations include the fact that many of the currently used standards are based on previous generations and thus may become flawed due to secular trends, increasing intermarriage, and global migration and do not reflect the modern population of the same geographical region [6]. The vast majority of refugees and asylum seekers hail from populations disproportionately underrepresented in published population standards. It is crucial that the individual conducting the assessment is aware of all these limitations and knows how to appropriately calculate the degrees of uncertainty.

Similar problems arise with other medically based examinations, such as the assessment of secondary sexual characteristics, such as breast development, pubic hair, or the laryngeal prominence in males, the onset of which are variable depending on numerous factors, such as ethnicity, geographical location, and even individual body morphology [6]. A study by Wu et al. [10] conducted on US girls of different ethnic backgrounds found African-American girls developing sexually dimorphic characteristics earlier than other ethnic groups, with 49.4% exhibiting breast bud development as early as aged 9, as compared to 24.5% in Hispanic girls and 15.8% of Caucasian girls of the same age [10]. They found similar trends with African-American boys being 1–2 years ahead of their Hispanic and Caucasian peers when it came to genital and pubic hair development. With regard to body shape, the study showed girls of a rounder (pyknic) physique to be on average 3 years ahead in physical development than their tall and lean (leptomorphic) peers. The reliability of age assessment based on these characteristics therefore remains questionable, especially when applying the same standards on ethnically and geographically diverse individuals. Commonly regarded as the most accurate indicator of chronological age in young children due to its close link to genetic rather than extrinsic factors, dental development also exhibits some of the same limitations for accurate aging than skeletal-based methods. Populations from differing geographic regions exhibit variations in the onset of tooth development, and factors such as migration introduce potential genetic variability into the age at which certain tooth development stages are achieved [6,11,12].

The United Nations High Commissioner for Refugees (UNHCR) suggests in its child asylum claim guidelines that the child’s psychosocial maturity needs to be taken into account in addition to physical indicators of age [13]. Psychological age is defined by the capacity of individuals to adapt to changing circumstances and includes the capacities of intelligence, learning, memory, skills, feelings, as well as motivations and emotions to apply behavioral control and self-regulation [14,15]. This psychological assessment needs to take into account the individual social history of the child, such as the culture and lifestyle, which familiar role the child played in its home country, the received education, economic status, etc. The UNHCR’s guidelines on child asylum claims suggest that in some cases in which persecution may have hindered an individual’s development and capacity for psychological maturity, they should be classified as a child even if chronological age slightly exceeds 18 years [13]. These guidelines, however, are not binding. An additional complicating factor is that there is a huge variation in the detail of assessment between countries which do incorporate these methods into the age estimation process; only in rare cases is the analysis conducted by a licensed psychologist, with cases more often being evaluated through interviews by immigration officers or social worker [6].

1.3 Age estimation of the dead

When dealing with unknown remains, the first priority of the case investigation is to determine the remains’ identity, since any forensic case would be hard to progress without the victim’s identification.

The first step in the identification process is to determine a biological profile assessing sex, ancestry, age, and stature, in order to obtain a general description of the unknown individual. This description will be submitted to the authorities to search for a suitable candidate fitting the established profile among the missing persons’ databases. The antemortem data from all candidates will be compared to the postmortem data obtained from the remains to achieve the individual’s identity.

The age estimation of decomposed or skeletonized human remains is one of the pillars of establishing a biological profile, thus playing a vital role in aiding the identification process or gaining insight into a population’s demographic, morbidity and mortality patterns. The latter, known as paleodemography, encompasses the identification of demographic parameters from archeological contexts [16]. Paleodemographic conclusions are based on the assumption that the mortality samples are an accurate reflection of the death rate of the analyzed population. Age estimations in these contexts tend to be either based on skeletal or dental indicators [17] and can be determined through morphological, histological, or biochemical criteria.

1.3.1 Age estimation of subadults

Age estimation based on skeletal remains is most accurate in subadults still undergoing the growth process. As already mentioned when pertaining to age estimation in the dead, the dental development is one of the key characteristics to determine chronological age [18]. As in the living, assessments can be carried out using radiographic evaluations of the root developments and mineralization or macroscopic observations of eruption patterns. The most commonly used standards include Moorrees et al. [19,20] and Demirjian et al. [21], both of which have sex-specific estimations based on a composite of radiographic and macroscopic images [18]. Whilst there are sex-specific variations in tooth development and eruption, having sex-specific standards pose a drawback in many cases, owing to the fact that sex estimation in subadults is not a straightforward matter and is likely to require genetic analyses. Another caveat of these methods is their derivation from Caucasian North American samples, resulting in inaccuracies when applying these to other populations [18]. Similar population restrictions apply to the Ubelaker system [22] and the London Atlas of tooth development [23], both providing schematic representation of tooth formations; the former based on a Native North American population, the latter on a mix of historic and modern British samples. Taking into consideration the above-mentioned limitations, pooled population standards have been suggested as a possible solution [18]. Another factor to take into consideration when using dental indicators for aging is the fact that most dental development is concluded by the age of 14 years, with only the third molars still evolving; which, however, vary markedly in their eruption time and are frequently congenitally absent [18].

Other than dentition, skeletal maturity is used to assess the age of juveniles. Skeletal maturity is derived from the measurements of bone size, shape, and degree of ossification; the latter including the size and the timing of appearing ossification centers as well as their eventual fusion [24–26]. Individual methods will not be listed at this stage, as they are detailed in another chapter within this volume (Chapter 5: Skeletal age estimation in adults, Black and Cunningham).

What should be mentioned at this stage, however, is that as discussed with regard to the age estimation of the living, while the stages of maturation each individual passes through are universal, the rate of skeletal maturity is affected by a number of factors. The limitations of commonly applied techniques include their derivation from skeletal collections or radiographic data of populations not representative of all ethnic groups and socioeconomic status [27]. Unlike the maturation of dentition, however, skeletal maturation is less fixed by genetic predisposition than dental eruption. Thus, although population differences occur, the socioeconomic factors play the largest role in variation [28–30]. Each individual has a genetically determined potential for growth and skeletal maturation. The maximum potential can be reached in optimal environmental conditions, whereas suboptimal environmental conditions, such as malnutrition, poor hygiene standards and higher morbidity, can lead to a delay in skeletal maturation and a stunting in overall growth [30]. Whether the ossification rate, however, is a one-generational or cross-generational record has to be determined in further studies. Even more so than is the case for the dentition, sex-specific differences in maturation rate need to be taken into consideration, which can pose some difficulties given the complexity of subadult sex determination.

1.3.2 Age estimation of adult individuals

The age estimation of adult human remains is a highly complex task. Some of the more traditionally used skeletal indicators for the aging of adults are based on morphological changes undergone by the bone due to the wear and tear of daily life as well as bone remodeling. These include the assessments of the pubic symphysis [31–37], the sternal rib ends [38], the auricular surface [39], or the clavicle [40]. The anatomist Todd was the first to study changes to the human pubic bone in the 1920s, and his system was since revised and built upon [37,41]. These skeletal degradation-based methods have several limitations. For one, whilst the predictable patterns and progression of skeletal morphological changes with increasing age are non-disputed, their linkage to age in years is not so straightforward. A variety of factors, such as genetic predisposition, health, nutrition, and manual labor, can have profound effects on the onset and timing of different morphological stages [31]. This variation can be observed between as well as within populations, and it is the latter, the individual-specific senescence, or aging, that is often underestimated [42]. Cranial suture closing, the fusion of the fibrous joints between the bones of the skull, has also been applied to the estimation of age. However, as estimations are in the order of 30 years or more, these techniques have generally been deemed too unreliable for use in forensic cases [18].

Other than the underlying biological factors, there are some limiting factors linked to the method of statistical analysis and data processing [17,42,43]. Methods which are based on single ordinal categorical variables are typically derived from a limited sample size (such as the six Suchey–Brooks stages), stating the mean age and the 95% confidence range within the stage [17]. Some, such as the original Suchey–Brooks classifications, do not include the standard errors of the 95% percentile. Konigsberg et al. [17] argue that the variables arising from sampling limitations in certain stages of the commonly used reference formulae may account for more of the perceived differences noted by researchers applying these to different populations than the actual variation in age structure between the population themselves. The authors further strongly advise against the use of percentile methods, suggesting progressional parametric models to be more applicable. Methodologies using linear regression in order to correlate a morphological score of an indicator to chronological age have also been found to be severely flawed, with systematic over estimation of age in young individual and under estimation in older individuals having been reported [42,43].

Similarly to anthropological methods for age estimation, while dental age estimation methods applied on subadults are based on growth and development, age estimation methods applied on adults are based on the degenerative changes of dental